1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to dithering for multi-toning. More particularly, the present invention relates to dithering for multi-toning, which can express a high-tone input image on a low-tone output device of M bits through dithering the high-tone input image of M+K bits.
2. Description of the Related Art
Digital devices that reproduce colors, such as a monitor, a scanner, a printer, and others, have diverse functions, an improved quality, and are using color space or color models, which are different according to each field of use. The color models can be divided into device-dependent models and device-independent models. Device-dependent models include the RGB model, an additive color space model, and the CMYK color model, a subtractive color space model, and device-independent models include the CIE L*a*b model, the CIE XYZ model, the CIE LUV model, and others. The CIE color model has been decided by the ICI (International Commission on Illumination), which decides standards on illuminators. The CIE XYZ color model expresses RGB tristimulus values as XYZ, a set of different, positive tristimulus values. Further, The CMYK color space is used in the printing field, and the RGB color space is used in computer monitors.
Further, when a high-tone input image is expressed on a low-tone output device, if it is not possible to use required colors, a dithering technique, which expresses similar colors by mixing as a set of dots of different-tone colors, is usually used. For example, in a display device or printing device, the whole image can be expressed using gray tones according to the rate of gray-color dots and white-color dots within a certain surface of the image, or can be expressed as pink multi-tones. The dithering technique is mainly used to heighten the realism of an image and to make an uneven and rough contour unnoticeable in a low-resolution output device.
The related art dithering technique has been mainly used to express an input image signal at a higher resolution than the resolution of an output device, and a spatial dithering or spatial-temporal dithering technique has been used to accomplish this. Because related art technologies using spatial dithering add noise, generated by a random generator, to the least significant bit (LSB) of an input image signal, the quality of the image deteriorates, which is a problem. Further, because related art technologies using spatial-temporal dithering use the same process on the RGB channel as the method of generating a dithered signal by, adding input signals to a regular mask pattern, a channel-overlap artifact or others are generated, which is a problem.